In view of the consumers' preference to 3C products with higher usability and portability, miniaturized electronic products with light weight and multiple functions have become the main trends in the market, which in turn motivates the development of three-dimensional (3D) integrated circuit (IC) and other circuit designs. With a 3D circuit device, complicated circuits can be formed on a circuit device having very limited volume, so that electronic products using same can have reduced volume without adversely affecting their functions. In other words, with a 3D circuit device, even a miniaturized electronic product can still be provided with complicated circuits. Therefore, 3D circuit devices indeed create the potential of producing miniaturized, light weight, compact and multifunctional electronic products, and are now widely applied to various products, such as mobile phones, automobile circuits, automated teller machine, and hearing aids.
Currently, there are different methods available for manufacturing a 3D circuit device. One of these methods is referred to as Molded Interconnect Device (MID)-Double Injection Molding process, in which a non-conductive material is first injection molded into a device carrier, and then, another type of material is injection molded to form a circuit pattern on the device carrier, and finally, metal conducting circuits are grown on the circuit pattern through chemical plating. Another method for manufacturing a 3D circuit device is referred to as the MID-LDS (Molded Interconnect Device-Laser Direct Structuring) process, in which a non-conductive plastic material containing catalyst is first injection molded into a device carrier, and then, the device carrier is exposed to laser light to activate the catalyst, so that the catalyst is converted into a catalyzed nuclear for reacting with ions of a pre-plating metal in a chemical plating reaction to form metal conducting circuits.
While the above-described conventional methods for forming 3D circuit device can be used to efficiently manufacture 3D circuit devices, the circuit pattern thereof often includes of a plurality of non-interconnected circuits and the metal coating for forming the metal conducting circuits of the 3D circuit device must be highly uniform in its thickness. In the chemical plating process, no electric power is applied; and the metal catalyst attached to some areas of the circuit device that are to be formed with the circuit pattern is used to react with ions of a pre-plating metal existing in the chemical plating solution in a catalytic reaction, so that the ions of the pre-plating metal are reduced on the areas of the circuit device for forming the circuit pattern. Compared to an electroplating process, the chemical plating process has the advantages of being free from the problem of unevenly distributed electric lines of force as well as being able to form metal coating with uniform thickness even if the circuit device to be plated has a very complicated geometrical shape. That is why the conducting circuits on the 3D circuit device are generally manufactured through chemical plating.
As having been mentioned above, in the chemical plating process, no electric power is applied; and the metal catalyst attached to some surfaces of the circuit device that are to be formed with the circuit pattern is used to react with ions of a pre-plating metal existing in the chemical plating solution in a catalytic reaction, so that the ions of the pre-plating metal are reduced on the areas of the circuit device for forming the circuit pattern. Therefore, it is able to form a metal coating of uniform thickness on the surfaces of the circuit device that are to be formed with the circuit pattern. However, since the chemical plating is a chemical reduction reaction occurred without externally applied energy, it requires longer reaction time and has relatively slow deposition speed, and will produce a large quantity of plating waste. For example, in the case of chemical plating, a reaction time longer than 3 or 4 hours is required to form a copper coating of about 10 μm in thickness or a nickel coating of about 3 μm in thickness. Further, the chemical plating requires a large quantity of plating solution and reductive agent, which will increase the manufacturing cost of the 3D circuit device.
On the other hand, a copper coating or a nickel coating of the same thickness can be formed at effectively reduced reaction time through electroplating to enable increased production efficiency. Meanwhile, in the electroplating process, much less amount of plating solution is used compared to the chemical plating; and the large quantity of reductive agent can also be omitted to lower the manufacturing cost. In addition, the plating solution used in the chemical plating has relatively poor stability compared to that used in the electroplating, and therefore requires troublesome procedures to maintain, condition and recycle the plating solution, which inevitably increases the material cost in the chemical plating. In view of the problems of slow reaction time and high material cost as found in the chemical plating process, it is desirable to effectively apply the electroplating process in the manufacturing of a 3D circuit device, so as to form various three-dimensional circuit patterns and form metal coating with uniform thickness to achieve the objectives of upgraded production efficiency, reduced manufacturing cost and reduced plating waste. In this way, it is possible to substitute the electroplating for the chemical plating in manufacturing the 3D circuit device.